Structural joint of two load carrying walls of a pressurized vessel

ABSTRACT

Disclosed herein is a structure that comprises a tank including an outer cylindrical surface and a domed end. The structure also comprises a tank skirt positioned circumferentially around the tank. A wall of the tank and a wall of the tank skirt form two sides of a y-joint between the tank and the tank skirt. The y-joint includes a wedge structure positioned between the tank and the tank skirt. Additionally, a thickness of at least one of the wall of the tank or the wall of the tank skirt forming the y-joint tapers such that the thickness of the at least one of the wall of the tank or the wall of the tank skirt that tapers has a greater thickness at the y-joint than away from the y-joint.

FIELD

This disclosure relates generally to pressurized vessels, and moreparticularly to designs and manufacturing methods for the structuraljoint of two load carrying walls of a pressurized vessel.

BACKGROUND

Stress risers, which are potentially structurally detrimental, usuallyoccur at a structural joint between the pressurized wall of a pressurevessel and another load carrying wall of the pressure vessel. Existingsolutions for reducing stress risers at such structural joints aremainly applicable to metallic pressure vessels. Solutions that helpreduce stress risers in metallic pressure vessels often are ineffectiveat reducing stress risers in pressure vessels made of compositestructures. Moreover, solutions designed to reduce stress risers incomposite pressure vessels require expensive, specialized materials.Accordingly, reducing stress risers, in wall junctions of pressurizedvessels made of composite materials, in an efficient, simple, andcost-effective manner is difficult.

SUMMARY

The subject matter of the present application has been developed inresponse to the present state of the art, and in particular, in responseto the problems and needs associated with stress risers (stresssingularity) that arise at the structural joint (also referred to asy-joint) of a pressure vessel's pressurized wall with another loadcarrying wall created when the pressure vessel wall is split into twobranches; one branch for a pressure retaining dome and a second branchwhich can interface with another structure. In general, the subjectmatter of the present application has been developed to provide designsand manufacturing methods for this structural joint of two load carryingwalls that overcome at least some of the above-discussed shortcomings ofthe prior art.

Disclosed herein is a structure that comprises a tank including an outercylindrical surface and a domed end. The structure also comprises a tankskirt positioned circumferentially around the tank. A wall of the tankand a wall of the tank skirt form two sides of a y-joint between thetank and the tank skirt. The y-joint includes a wedge structurepositioned between the tank and the tank skirt. Additionally, athickness of at least one of the wall of the tank or the wall of thetank skirt forming the y-joint tapers such that the thickness of the atleast one of the wall of the tank or the wall of the tank skirt thattapers has a greater thickness at the y-joint than away from they-joint. The preceding subject matter of this paragraph characterizesexample 1 of the present disclosure.

The thickness of the wall of the tank forming the y-joint tapers. Thepreceding subject matter of this paragraph characterizes example 2 ofthe present disclosure, wherein example 2 also includes the subjectmatter according to example 1, above.

A thickness of the wall of the tank forming the y-joint is greater alonga length of the y-joint and a length extending beyond each side of they-joint than further away from the y-joint. The preceding subject matterof this paragraph characterizes example 3 of the present disclosure,wherein example 3 also includes the subject matter according to example2, above.

The tank comprises a lay-up of plies. A ply drop-off ratio of the lay-upof plies along the y-joint is not less than 30:1. The preceding subjectmatter of this paragraph characterizes example 4 of the presentdisclosure, wherein example 4 also includes the subject matter accordingto example 3, above.

The thickness of the wall of the tank skirt forming the y-joint tapers.The preceding subject matter of this paragraph characterizes example 5of the present disclosure, wherein example 5 also includes the subjectmatter according to any one of examples 1-4, above.

A thickness of the wall of the tank skirt forming the y-joint is greateralong a length of the y-joint and a length extending beyond each side ofthe y-joint than further away from the y-joint. The preceding subjectmatter of this paragraph characterizes example 6 of the presentdisclosure, wherein example 6 also includes the subject matter accordingto example 5, above.

A stiffness of the wall of the tank and a stiffness of the wedgestructure are substantially the same. The preceding subject matter ofthis paragraph characterizes example 7 of the present disclosure,wherein example 7 also includes the subject matter according to any oneof examples 1-6, above.

The thickness of the wall of the tank forming the y-joint tapers. Thethickness of the wall of the tank skirt forming the y-joint tapers. Thepreceding subject matter of this paragraph characterizes example 8 ofthe present disclosure, wherein example 8 also includes the subjectmatter according to any one of examples 1-7, above.

The tank and the wedge structure are constructed from materials from asame family of composite materials in different forms. The tankcomprises tape and the wedge structure comprises fabric. The precedingsubject matter of this paragraph characterizes example 9 of the presentdisclosure, wherein example 9 also includes the subject matter accordingto any one of examples 1-8, above.

The lay-up of the wedge structure is a constructed such that a firstfabric ply of the wedge structure is oriented in a different directionto a second fabric ply adjacent to the first fabric ply. The precedingsubject matter of this paragraph characterizes example 10 of the presentdisclosure, wherein example 10 also includes the subject matteraccording to any one of examples 1-9, above.

The fabric ply nearest the tank is oriented forty-five degrees relativeto the axial direction of the tank. The preceding subject matter of thisparagraph characterizes example 11 of the present disclosure, whereinexample 11 also includes the subject matter according to any one ofexamples 1-10, above.

The tank is a pressurized vessel. The preceding subject matter of thisparagraph characterizes example 12 of the present disclosure, whereinexample 12 also includes the subject matter according to any one ofexamples 1-11, above.

The tank is a composite cryogenic fuel tank. The preceding subjectmatter of this paragraph characterizes example 13 of the presentdisclosure, wherein example 13 also includes the subject matteraccording to any one of examples 1-12, above.

The structure forms part of a spacecraft. The preceding subject matterof this paragraph characterizes example 14 of the present disclosure,wherein example 14 also includes the subject matter according to any oneof examples 1-13, above.

Also disclosed herein is a structure within a spacecraft. The structureincludes a pressurized tank including an outer cylindrical surface and adomed end. The structure also includes a tank skirt positionedcircumferentially around the pressurized tank. A wall of the pressurizedtank and a wall of the tank skirt form two sides of a y-joint betweenthe pressurized tank and the tank skirt. The y-joint includes a wedgestructure positioned between the pressurized tank and the tank skirt. Athickness of the wall of the pressurized tank forming the y-joint taperssuch that the thickness of the wall of the pressurized tank has agreater thickness at the y-joint than away from the y-joint. The wedgestructure comprises a lay-up of multiple fabric plies. The lay-up ofmultiple fabric plies of the wedge structure comprises a first fabricply and a second fabric ply, oriented in a different direction than thefirst fabric ply. The preceding subject matter of this paragraphcharacterizes example 15 of the present disclosure.

The first fabric ply is nearer the pressurized tank than the secondfabric ply. The first fabric ply is oriented forty-five degrees relativeto an axial direction of the tank. The preceding subject matter of thisparagraph characterizes example 16 of the present disclosure, whereinexample 16 also includes the subject matter according to example 15,above.

Also disclosed herein is a method that comprises laying-up a wedgestructure at a tapered thickness portion of a domed end of the tankafter the tank has been cured. The method additionally includes curingthe wedge structure after being laid-up at the domed end of the tank.The method also includes laying-up a tank skirt around the wedgestructure and the tank, after curing the wedge structure, such that awall of the tank and a wall of the tank skirt form two sides of ay-joint between the tank and the tank skirt within which the wedgestructure is located. The preceding subject matter of this paragraphcharacterizes example 17 of the present disclosure.

The step of laying-up the wedge structure includes orienting a firstfabric ply of the wedge structure in a different direction than a secondfabric ply adjacent to the first fabric ply. The preceding subjectmatter of this paragraph characterizes example 18 of the presentdisclosure, wherein example 18 also includes the subject matteraccording to example 17, above.

A fabric ply of the wedge structure nearest the tank is orientedforty-five degrees relative to an axial direction of the tank. Thepreceding subject matter of this paragraph characterizes example 19 ofthe present disclosure, wherein example 19 also includes the subjectmatter according to any one of examples 17 or 18, above.

The laying-up the tank skirt around the wedge structure and the tankfurther includes tapering a thickness of the tank skirt such that thethickness of the tank skirt is greater at the y-joint than away from they-joint. The preceding subject matter of this paragraph characterizesexample 20 of the present disclosure, wherein example 20 also includesthe subject matter according to any one of examples 17-19, above.

The described features, structures, advantages, and/or characteristicsof the subject matter of the present disclosure may be combined in anysuitable manner in one or more embodiments and/or implementations. Inthe following description, numerous specific details are provided toimpart a thorough understanding of embodiments of the subject matter ofthe present disclosure. One skilled in the relevant art will recognizethat the subject matter of the present disclosure may be practicedwithout one or more of the specific features, details, components,materials, and/or methods of a particular embodiment or implementation.In other instances, additional features and advantages may be recognizedin certain embodiments and/or implementations that may not be present inall embodiments or implementations. Further, in some instances,well-known structures, materials, or operations are not shown ordescribed in detail to avoid obscuring aspects of the subject matter ofthe present disclosure. The features and advantages of the subjectmatter of the present disclosure will become more fully apparent fromthe following description and appended claims, or may be learned by thepractice of the subject matter as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the subject matter may be more readilyunderstood, a more particular description of the subject matter brieflydescribed above will be rendered by reference to specific embodimentsthat are illustrated in the appended drawings. Understanding that thesedrawings depict only typical embodiments of the subject matter and arenot therefore to be considered to be limiting of its scope, the subjectmatter will be described and explained with additional specificity anddetail through the use of the drawings, in which:

FIG. 1 is a cross-sectional view of a y-joint between a tank and a tankskirt, according to one or more embodiments of the present disclosure;

FIG. 2 is an internal side view of a launch vehicle showing locations ofy-joints of pressurized vessels, according to one or more embodiments ofthe present disclosure;

FIG. 3 is an internal perspective view of a launch vehicle showinglocations of y-joints of pressurized vessels, according to one or moreembodiments of the present disclosure;

FIG. 4 is a cross-sectional view of a y-joint between a tank and a tankskirt, according to one or more embodiments of the present disclosure;

FIG. 5 is a perspective view of a pressurized tank, according to one ormore embodiments of the present disclosure;

FIG. 6 is a close-up perspective view of a pressurized tank, accordingto one or more embodiments of the present disclosure;

FIG. 7 is a close-up perspective view of a pressurized tank, accordingto one or more embodiments of the present disclosure;

FIG. 8 is a close-up perspective view of a pressurized tank, accordingto one or more embodiments of the present disclosure;

FIG. 9 is a close-up perspective view of a pressurized tank and tankskirt, according to one or more embodiments of the present disclosure;

FIG. 10 is a perspective view of a pressurized tank and tank skirt,according to one or more embodiments of the present disclosure;

FIG. 11 is a cross-sectional side view of a wedge structure, accordingto one or more embodiments of the present disclosure; and

FIG. 12 is a schematic flow diagram of a method, according to one ormore embodiments of the present disclosure.

DETAILED DESCRIPTION

Reference throughout this specification to “one embodiment,” “anembodiment,” or similar language means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment of the present disclosure.Appearances of the phrases “in one embodiment,” “in an embodiment,” andsimilar language throughout this specification may, but do notnecessarily, all refer to the same embodiment. Similarly, the use of theterm “implementation” means an implementation having a particularfeature, structure, or characteristic described in connection with oneor more embodiments of the present disclosure, however, absent anexpress correlation to indicate otherwise, an implementation may beassociated with one or more embodiments.

Referring to FIG. 1, one example of a conventional y-joint 12 between atank 14 and a tank skirt 16 is shown. The conventional y-joint 12includes a softening strip 18 between the tank 14 and the tank skirt 16.The softening strip 18 includes a relative stiffness well below thestiffness of the tank 14 or the tank skirt 106 in many instances. Asdescribed in more detail below, the y-joint 12 will include stressconcentrations. A stress concentration, or stress riser, is susceptibleto forming at a first location 19 as well as at a second location 17.

The relative forces that are exerted on the pressurized wall of the tank14 in conjunction with another load carrying wall of the tank skirt 16give rise to structurally detrimental stresses (or stress singularities,stress concentrations, or stress risers) at the first location 19 andthe second location 17. Some existing solutions to compensate for thestress concentrations in metallic structures include welded or boltedconnections. Such solutions are not effective with composite structures.In addition, bolts or welded connections are susceptible to leaking,which can create a dangerous situation if the tank 14 is pressurized andfilled with a highly combustible material as is often the case.

As shown in FIG. 1, one existing solution for reducing stressconcentrations in composite structures uses special materials in theform of the softening strip 18. In such solutions, a material (usuallyof some composite preform in case of cryogenic temperatures, or rubberfor other temperature ranges) is designed and manufactured to be muchsofter compared to the stiffness of the adjoining walls of the tank 14and the tank skirt 16. The objective is to gradually reduce the stressesat the point of stress concentrations of the joint. Such materials areexpensive and difficult to develop and manufacture for cryogenicapplications. Moreover, rubber-like materials are not applicable tocryogenic applications or may be too soft at other temperature ranges.In addition, the use of softening strips 18 often requires excessivetrial and error experimentation because the stiffness (especially incryogenic temperatures) cannot always be predicted accurately.

Embodiments described herein allow for a more robust and cost efficientdesign for reducing stress concentrations in the joint between a wall ofa pressure vessel and an adjoining load carrying wall (which may bepressurized or not pressurized) compared to conventional techniques.More specifically, embodiments described herein include a thirdadjoining member at the joint between load carrying walls and/or employgradual tailoring of the thickness and lay-up of one or both of the loadcarrying walls.

Referring to FIGS. 2 and 3, two examples of a spacecraft 101, includingvarious locations of y-joints 102 are shown. In these examples, they-joints 102 are the joints between domed tanks and tank skirts. Thetank skirts may form a structural component, such as an exteriorsidewall, of the spacecraft 101. The extreme conditions, includingcryogenic conditions, that the spacecraft 101 may be subjected torequire proper load sharing between the walls on each side of they-joints 102.

Referring now to FIG. 4, according to some examples of the presentdisclosure, a cross-sectional view of a structure 100, including ay-joint 102 between a tank 120 and a tank skirt 110, is shown. In someembodiments, the tank 120 is a vessel with an outer cylindrical surface122 and one or two domed ends 124 (see, for example, FIG. 5). The lengthof the tank 120 may vary as is shown in the varying sized tanks 120, andcorresponding tank skirts 110, depicted in FIGS. 2 and 3. In someembodiments, the tanks 120 include two domed ends 124 and will, inconjunction with one or more tank skirts 110, form annular or continuousy-joints 102.

As has been described herein, in some embodiments, the tank 120 formspart of a spacecraft or a launch vehicle and is subject to cryogenic orother extreme space or launch conditions. In some embodiments, the tank120 is made of a composite material, which, as used herein, includesfiber reinforced polymer materials. The tank 120 may be a pressurizedtank and may be referred to as a pressurized vessel or pressure vessel.In some embodiments, the tank 120 houses a combustible material, such asliquid oxygen, liquid hydrogen, liquid methane, or other fuels underpressure.

The structure 100 includes a tank skirt 110 coupled to the tank 120. Thetank skirt 110 includes an inner cylindrical surface 112 that couples tothe outer cylindrical surface 122 of the tank 120. The tank skirt 110,in some embodiments, is made of a composite material, which can be thesame as or different than the composite material of the tank 120. Thetank skirt 110 may form a structural part of an aircraft, a spacecraft,or part of a rocket or launch vehicle (see, generally, FIGS. 2 and 3).The tank skirt 110 is bonded to or otherwise integrated (e.g.,co-formed) with the tank 120.

As the tank 120 transitions from the outer cylindrical surface 122 tothe domed end 124, the tank 120 and the tank skirt 110 form a y-joint102 where the wall of the tank 120 diverges from the wall of the tankskirt 110. Accordingly, the wall of the tank 120 and the wall of thetank skirt 110 form two opposite sides of the y-joint 102. The y-joint122 extends continuously around a circumference of the tank 120 and maygenerally be considered to define a space, having a substantiallytriangular cross-sectional shape along a plane parallel to a centralaxis of the tank 120, between the tank 120 and the tank skirt 110.Stress concentrations at and near the y-joint 102 should be accountedfor to ensure the tank 120 and the tank skirt 110 are structurallysound. The embodiments of the present disclosure account for such stressconcentrations without excessive cost and weight and enable the designand manufacturing of composite y-joints without the need forexperimental verification of the structural properties.

According to one embodiment, shown in FIG. 4, the stress concentrationsare accounted for with a wedge structure 140 positioned between the tank120 and the tank skirt 110. The wedge structure 140 extends annularly orcontinuously around a circumference of the tank 120 within the spacedefined by the y-joint 102. The wedge structure 140, in someembodiments, is made of a composite material. In some embodiments, thewedge structure 140 is constructed of the same material as the tank 120or a same composite material family. However, in some implementations,notwithstanding material being the same, it may be in a different formcompared to that of the tank 120. For example, the tank 120 may beconstructed of a tape and the wedge structure may be constructed of afabric both from the same constituents (matrix and fiber). Compositematerial “families” have the same basic constituents, fiber and matrix,but different forms may be created (tape, fabric, and other slightvariations such as slit tape that may only be ⅛″ wide versus wide tapethat may be 2″ wide) which allow for different manufacturing processes(hand layup, automated tape placement, fiber placement, etc). Eachcomposite in the family is made from the same or similar constituentsand the forms are compatible with one another such that they can be usedtogether, e.g. you can put a cloth ply with a tape ply in a laminate.

In some embodiments, the size of the wedge structure 140 may be muchsmaller than that of a softening strip 18, such as the one shown inFIG. 1. The dimensions of the wedge structure can be on the order ofonly one-fifth that of the dimensions of a softening strip.

In some embodiments, a stiffness of the wall of the tank 120 and/or thetank skirt 110 and the wedge structure 140 is substantially the same. Asused herein, in the context of stiffness, substantially the same meansfalls in the same range or in the same order of magnitude. For instancethe stiffness of the tank wall may be 5 msi (1 million pounds per squareinch) in the axial direction and 10 msi in hoop direction; whereas thestiffness of the wedge structure 140 may be 7 msi in both directions.Generally, the stiffness of the tank 120 and the wedge structure 140 isbetween 5 msi and 10 msi, in some examples. In another particularexample, the stiffness of the tank 120 is 6.6 msi in the axialdirection, 8.18 msi in the hoop direction, and the stiffness of thewedge structure 140 is 6.5 msi. The stiffness of the wedge structure140, being substantially the same as the tank 120 and/or the tank skirt110, allows the wedge structure 140 to be formed of a material similarto that of the tank 120 and/or the tank skirt 110, which allows for theuse of cheaper materials than those used for specialized cryogenicsoftening strips. In contrast, softening strips such as described inFIG. 1 have stiffness values that are orders of magnitude lower than thetank, e.g. 0.1 msi.

The wedge structure 140 may be bonded to both the tank 120 and the tankskirt 110 by an adhesive 130. The size of the adhesive 130 in FIG. 4 isexaggerated and not necessarily to scale for clarity in showing theadhesive 130. The adhesive 130 may be a glue or a film adhesive. In someembodiments, the adhesive 130 extends beyond the ends of the wedgestructure 140 as depicted. The adhesive 130 may extend beyond the end ofthe wedge structure 140 at the open end of the y-joint 102 as well as atthe closed end of the y-joint 102 (or what is sometimes referred to asthe crotch) such that the adhesive 130 also, at least partially, adheresthe tank skirt 110 directly to the outer cylindrical surface 122 of thetank 120. The crotch may be filled with additional adhesive 130 toensure no separation between the tank 120 and the tank skirt 110 occurswhere the wedge structure 140 ends.

In addition to the wedge structure 140, a reduction in stressconcentrations is facilitated by a tapered wall thickness of the tank120. The wall thickness of the tank 120 increases at the y-joint 102. Asdepicted, a wall thickness 127 of the wall defining the cylindricalsurface 122 of the tank 120 increases to a wall thickness 129 of thewall defining the domed end 124. Accordingly, the wall thickness 129 ofthe tank 120 is greater at the y-joint 102 than at the cylindricalsurface 122. The wall thickness may again taper or decrease away fromthe y-joint 102 toward a point of the domed end 124, such that the wallthickness of the domed end 124 away from the y-joint 102 is the same asor considerably less than the wall thickness of the wall definingcylindrical surface 122. The tapering of the wall thickness at they-joint 102 allows for the tank 120, wedge structure 140, and the tankskirt 110 to be structurally sound at locations 107, 109 where stressconcentrations are susceptible to occur. Without the presence of thewedge, there would be detrimental stress concentration at 102. But, withthe wedge, the stress concentration is divided between points 107 and109. Those stress concentrations are further minimized by tapering thewall thickness. The thickness of the tank wall and the size (e.g.,height and length) of the wedge structure 140 can be optimized orconcurrently sized depending on the application conditions of thestructure 100.

The tank 120 may be constructed by lay-up of plies to create thethickness of the tank walls and the tapering occurs with the increase inplies at the y-joint 102. The ply drop-off ratio may vary depending onthe application conditions of the structure 100 but, in someembodiments, the ply drop-off ratio of the tank lay-up should not beless than 30:1.

In some embodiments, the tapering occurs at the y-joint 102. In someembodiments, the tapering occurs beyond each side of the y-joint 102such that the greater thickness extends beyond the y-joint 102.

As depicted in FIG. 4, the tank wall thickness tapers while the tankskirt wall thickness remains constant. However, in other embodiments,the tank skirt wall defining the y-joint 102 tapers in thickness. Thatis, the wall thickness of the wall of the tank skirt 110 tapers with agreater thickness at the y-joint 102 and with the wall thickness of thetank 120 remaining constant. Either side of the y-joint 102 may taper inthickness depending on the application conditions. In some embodiments,the wall thickness of the tank 120 and the tank skirt 110 defining bothsides of the y-joint 102 may taper. That is, both the tank wall and thetank skirt wall may taper in thickness with a greater thickness of thewalls being at the y-joint 102.

Depending on the application, various forces or loads may be exerted onthe structure 100. FIG. 4 depicts a skirt load 116 opposite a tank domeload 126. The varying loads will contribute to the stress concentrations107, 109 at the y-joint 102 and will factor into to the sizingrequirements for the wall thickness tapering and the wedge structure140.

The tapering of the thickness allows for the gradual sharing of theloads between the tank 120 and the tank skirt 110 by maintainingadequate thickness on at least one side of the y-joint 102 or both sidesof the y-joint 102.

Referring now to FIG. 5, a perspective view of a tank 120 is shown. Thetank 120 includes an outer cylindrical surface 122 and a domed end 124.Also depicted is an adhesive 130 which is placed around thecircumference of the tank 120. The adhesive 130 extends onto the outercylindrical surface 122 and onto the domed end 124 a length greater thanwhere the wedge structure will be placed. FIG. 5 further depicts theaxial direction 121 of the tank 120.

Referring now to FIG. 6, a close-up view of the tank 120 and adhesive130 are shown. FIG. 6 further depicts a cross section of the tank wall.As discussed in other embodiments, the thickness of the tank wall taperswith a greater thickness at the area of the y-joint (depicted by arrows129) than the thickness nearer the top of the domed end (depicted byarrows 127). Referring still to FIG. 6, tank 120, in some embodiments,is cured prior to laying the adhesive 130.

Referring to FIG. 7, the wedge structure 140 is then laid up on theadhesive 130 around the circumference of the tank 120. The wedgestructure 140 may be formed as depicted generally in FIG. 11, withfabric plies 142 of varying length allowing for a generally triangleshape to emerge. The length 144 of the wedge structure 140 and theheight 146 of the wedge structure can be tailored depending on the need.

In some embodiments, the plies are fabric plies 142. In otherembodiments, the plies may be tape plies. Referring to FIG. 11, eachfabric ply layer may be oriented in a different direction than thefabric ply layer above and/or below. Referring to FIG. 7, an orientationof the fabric ply at zero degrees relative to the axial direction of thetank is shown generally at 147. An orientation of the fabric ply atforty-five degrees relative to the axial direction of the tank is showngenerally at 149.

The orientation of the fabric plies 142 may be adjusted at any angleincluding angles between the two shown in FIG. 7. In some embodiments,the fabric ply 142 nearest the adhesive layer 130 may be generally laidup at forty-five degrees. Testing indicates that such an orientationreduces the bonded interface stiffness in the load direction (which maybe parallel to the axial direction 121).

In some embodiments, a lay-up of the wedge structure 140 is aconstructed such that a first fabric ply 142 of the wedge structure 140is oriented in a different direction to a second fabric ply 142 adjacentto the first fabric ply 142. In some embodiments, the orientation of theindividual fabric plies 142 of the wedge structure 140 are laid up in analternating or sequenced pattern, varying from forty-five degreesrelative to the axial direction 121 of the tank 120 to zero degreesrelative to the axial direction 121 of the tank 120. In someimplementation, the orientations may alternate between two orientations.

In other implementations, the orientations may vary in a predeterminedsequence of orientations. For example, in some implementations, theorientation of the fabric plies 142 may be sequenced such thattwo-thirds of the fabric plies are oriented at forty-five degrees andone-third of the fabric plies are oriented at zero degrees.

Referring again to FIG. 7, after the lay-up of the wedge structure 140,the wedge structure 140 is cured to form a composite material. In someembodiments, the wedge structure 140 is a same material as the tank 120.In some embodiments, the wedge structure 140 is a similar material asthe tank 120. In some embodiments, they are the same material in adifferent form, where the tank 120 is constructed of a tape and thewedge structure 140 is constructed of a fabric.

Referring now to FIG. 8, an adhesive 130 is applied to the wedgestructure 140 and extending beyond to the outer cylindrical surface ofthe tank 120. The adhesive 130 will be used to bond the wedge structure140 to the tank skirt 110 as well as to bond the outer cylindricalsurface of the tank 120 to the tank skirt 110.

Referring now to FIG. 9, the tank skirt 110 is laid up over the adhesive130 and wedge structure 140. The tank skirt 110 extends beyond the wedgestructure 140 and forms one side of the y-joint 102. Referring to FIG.10, a perspective view of the tank 120 and tank skirt 110 is shown. Asshown, the tank skirt 110 only extends beyond the one domed end 124 ofthe tank 120. In some embodiments, the tank skirt 110 may extend beyondboth domed ends 124 of the tank 120 such that there are two y-joints 102formed between the tank 120 and the tank skirt 110, one on each domedend 124 of the tank 120.

Embodiments disclosed herein utilize a third member, the wedge structure140, at the junction between two load carrying walls, the tank 120 andthe tank skirt 110. The size and lay-up of the wedge structure 140 maybe optimized in conjunction with the thickness of the adjacent walls tomake the joint work. Such embodiments do not require the use of specialmaterials. The stiffness of the wedge structure 140 can be manufacturedfrom composite material layers of the same or very similar layers as thetwo primary adjoining walls of the structural joint. The use of materialsimilar to that of the adjoining walls results in similar coefficient ofthermal expansion which helps to avoid the development of detrimentalstresses due to thermal contraction/expansion. Any stiffness tailoringof the wedge structure 140 can be achieved by the appropriate layerorientation and the size and shape of the wedge structure 140. Thestiffness of the wedge structure 140 is comparable to the adjoiningwalls such that it also carries significant load and therefore performsthe function of transforming the one high stress concentration to twostress concentrations of lower intensity.

In addition to the introduction of the wedge structure 140 of a similarmaterial, embodiments described herein may achieve the proper loadsharing between the two load carrying walls by gradually increasingand/or decreasing the thickness of one wall versus the other such that,at the point where the two walls are joined, the load sharing is at aratio that is not detrimental to the joint.

Now referring to FIG. 12, one embodiment of a method 500 is shown. Themethod 500 includes laying-up 502 a wedge structure at a domed end of analready cured composite material tank. At 504, the method 500 includescuring the wedge structure. The method further includes laying-up a tankskirt around the wedge structure and tank at 506, wherein a wall of thetank and a wall of the tank skirt form two sides of a y-joint betweenthe tank and the tank skirt. The tank includes a tapered wall thicknesswith a greater thickness at the y-joint. The method then ends.

In some embodiments, the method may further include concurrently sizinga length and a height of the wedge structure along with the thickness ofthe tank at the y-joint. Depending on the parameters of use of thestructure, the size of the wedge structure as well as the taper ratio ofthe tank wall or the tank skirt wall can be optimized while minimizingthe amount of material needed and the overall weight of the structure.Considerations may include the pressure in the tank and the ambientpressures on the tank skirt.

In some embodiments, the method may include laying an adhesive layer onthe tank prior to laying-up the wedge structure. In some embodiments,the laying-up the wedge structure includes laying-up fabric plies. Thefabric plies may include an orientation. In some embodiments, theorientation of the fabric ply adjacent to the adhesive layer is angledrelative to the axial direction of the tank. In some implementations,the orientation of the fabric ply adjacent to the adhesive layer isforty-five degrees relative to the axial direction of the tank. In someembodiments, the orientation of the fabric ply adjacent to the adhesivelayer is between five degrees and eighty-five degrees relative to theaxial direction of the tank. The angled fabric plies at the bondedinterface between the wedge structure and the tank reduces the bondedinterface stiffness in the load direction.

In some embodiments, the orientation of the individual fabric plies ofthe wedge structure are laid up in an alternating or sequenced pattern,varying from forty-five degrees relative to the axial direction of thetank to zero degrees relative to the axial direction of the tank. Theorientations may alternate, in some implementations. In otherimplementations, the orientations may vary in another predeterminedsequence.

In some embodiments, the method may include laying-up the tank skirtaround the wedge structure and the tank further includes tapering a wallthickness of the tank skirt with a greater thickness at the y-joint.

Although described in a depicted order, the method may proceed in any ofa number of ordered combinations.

In the above description, certain terms may be used such as “up,”“down,” “upper,” “lower,” “horizontal,” “vertical,” “left,” “right,”“over,” “under” and the like. These terms are used, where applicable, toprovide some clarity of description when dealing with relativerelationships. But, these terms are not intended to imply absoluterelationships, positions, and/or orientations. For example, with respectto an object, an “upper” surface can become a “lower” surface simply byturning the object over. Nevertheless, it is still the same object.Further, the terms “including,” “comprising,” “having,” and variationsthereof mean “including but not limited to” unless expressly specifiedotherwise. An enumerated listing of items does not imply that any or allof the items are mutually exclusive and/or mutually inclusive, unlessexpressly specified otherwise. The terms “a,” “an,” and “the” also referto “one or more” unless expressly specified otherwise. Further, the term“plurality” can be defined as “at least two.”

Additionally, instances in this specification where one element is“coupled” to another element can include direct and indirect coupling.Direct coupling can be defined as one element coupled to and in somecontact with another element. Indirect coupling can be defined ascoupling between two elements not in direct contact with each other, buthaving one or more additional elements between the coupled elements.Further, as used herein, securing one element to another element caninclude direct securing and indirect securing. Additionally, as usedherein, “adjacent” does not necessarily denote contact. For example, oneelement can be adjacent another element without being in contact withthat element.

As used herein, the phrase “at least one of”, when used with a list ofitems, means different combinations of one or more of the listed itemsmay be used and only one of the items in the list may be needed. Theitem may be a particular object, thing, or category. In other words, “atleast one of” means any combination of items or number of items may beused from the list, but not all of the items in the list may berequired. For example, “at least one of item A, item B, and item C” maymean item A; item A and item B; item B; item A, item B, and item C; oritem B and item C. In some cases, “at least one of item A, item B, anditem C” may mean, for example, without limitation, two of item A, one ofitem B, and ten of item C; four of item B and seven of item C; or someother suitable combination.

Unless otherwise indicated, the terms “first,” “second,” etc. are usedherein merely as labels, and are not intended to impose ordinal,positional, or hierarchical requirements on the items to which theseterms refer. Moreover, reference to, e.g., a “second” item does notrequire or preclude the existence of, e.g., a “first” or lower-numbereditem, and/or, e.g., a “third” or higher-numbered item.

As used herein, a system, apparatus, structure, article, element,component, or hardware “configured to” perform a specified function isindeed capable of performing the specified function without anyalteration, rather than merely having potential to perform the specifiedfunction after further modification. In other words, the system,apparatus, structure, article, element, component, or hardware“configured to” perform a specified function is specifically selected,created, implemented, utilized, programmed, and/or designed for thepurpose of performing the specified function. As used herein,“configured to” denotes existing characteristics of a system, apparatus,structure, article, element, component, or hardware which enable thesystem, apparatus, structure, article, element, component, or hardwareto perform the specified function without further modification. Forpurposes of this disclosure, a system, apparatus, structure, article,element, component, or hardware described as being “configured to”perform a particular function may additionally or alternatively bedescribed as being “adapted to” and/or as being “operative to” performthat function.

The schematic flow chart diagram included herein is generally set forthas logical flow chart diagrams. As such, the depicted order and labeledsteps are indicative of one embodiment of the presented method. Othersteps and methods may be conceived that are equivalent in function,logic, or effect to one or more steps, or portions thereof, of theillustrated method. Additionally, the format and symbols employed areprovided to explain the logical steps of the method and are understoodnot to limit the scope of the method. Although various arrow types andline types may be employed in the flow chart diagrams, they areunderstood not to limit the scope of the corresponding method. Indeed,some arrows or other connectors may be used to indicate only the logicalflow of the method. For instance, an arrow may indicate a waiting ormonitoring period of unspecified duration between enumerated steps ofthe depicted method. Additionally, the order in which a particularmethod occurs may or may not strictly adhere to the order of thecorresponding steps shown.

The present subject matter may be embodied in other specific formswithout departing from its spirit or essential characteristics. Thedescribed embodiments are to be considered in all respects only asillustrative and not restrictive. All changes which come within themeaning and range of equivalency of the claims are to be embraced withintheir scope.

What is claimed is:
 1. A structure for containing a substance, thestructure comprising: a tank comprising an outer cylindrical surface anda domed end; and a tank skirt positioned circumferentially around thetank, wherein a wall of the tank and a wall of the tank skirt form twosides of a y-joint between the tank and the tank skirt; wherein: they-joint comprises a wedge structure positioned between the tank and thetank skirt; and a thickness of at least one of the wall of the tank orthe wall of the tank skirt forming the y-joint tapers such that thethickness of the at least one of the wall of the tank or the wall of thetank skirt that tapers has a greater thickness at the y-joint than awayfrom the y-joint.
 2. The structure according to claim 1, wherein thethickness of the wall of the tank forming the y-joint tapers.
 3. Thestructure according to claim 2, wherein a thickness of the wall of thetank forming the y-joint is greater along a length of the y-joint and alength extending beyond each side of the y-joint than further away fromthe y-joint.
 4. The structure according to claim 3, wherein: the tankcomprises a lay-up of plies; and a ply drop-off ratio of the lay-up ofplies along the y-joint is not less than 30:1.
 5. The structureaccording to claim 1, wherein the thickness of the wall of the tankskirt forming the y-joint tapers.
 6. The structure according to claim 5,wherein a thickness of the wall of the tank skirt forming the y-joint isgreater along a length of the y-joint and a length extending beyond eachside of the y-joint than further away from the y-joint.
 7. The structureaccording to claim 1, wherein a stiffness of the wall of the tank and astiffness of the wedge structure are substantially the same.
 8. Thestructure according to claim 1, wherein: the thickness of the wall ofthe tank forming the y-joint tapers; and the thickness of the wall ofthe tank skirt forming the y-joint tapers.
 9. The structure according toclaim 1, wherein: the tank and the wedge structure are constructed ofmaterials from a same family of composite materials in different forms;the tank comprises tape; and the wedge structure comprises fabric. 10.The structure according to claim 9, wherein a lay-up of the wedgestructure is a constructed such that a first fabric ply of the wedgestructure is oriented in a different direction to a second fabric plyadjacent to the first fabric ply.
 11. The structure according to claim10, wherein a fabric ply nearest the tank is oriented forty-five degreesrelative to the axial direction of the tank.
 12. The structure accordingto claim 1, wherein the tank is a pressurized vessel.
 13. The structureaccording to claim 1, wherein the tank is a composite cryogenic fueltank.
 14. The structure according to claim 1, wherein the structureforms part of a spacecraft.
 15. A structure for containing a pressurizedsubstance, the structure comprising: a pressurized tank comprising anouter cylindrical surface and a domed end; and a tank skirt positionedcircumferentially around the pressurized tank, wherein a wall of thepressurized tank and a wall of the tank skirt form two sides of ay-joint between the pressurized tank and the tank skirt; wherein: they-joint comprises a wedge structure positioned between the pressurizedtank and the tank skirt; a thickness of the wall of the pressurized tankforming the y-joint tapers such that the thickness of the wall of thepressurized tank has a greater thickness at the y-joint than away fromthe y-joint; the wedge structure comprises a lay-up of multiple fabricplies; and the lay-up of multiple fabric plies of the wedge structurecomprises a first fabric ply and a second fabric ply, oriented in adifferent direction than the first fabric ply.
 16. The structureaccording to claim 15, wherein: the first fabric ply is nearer thepressurized tank than the second fabric ply; and the first fabric ply isoriented forty-five degrees relative to an axial direction of the tank.17. A method of integrating a wall skirt and a tank, each made ofcomposite materials, the method comprising: laying-up a wedge structureat a tapered thickness portion of a domed end of the tank after the tankhas been cured; curing the wedge structure after being laid-up at thedomed end of the tank; and laying-up a tank skirt around the wedgestructure and the tank, after curing the wedge structure, such that awall of the tank and a wall of the tank skirt form two sides of ay-joint between the tank and the tank skirt within which the wedgestructure is located.
 18. The method according to claim 17, wherein thestep of laying-up the wedge structure comprises orienting a first fabricply of the wedge structure in a different direction than a second fabricply adjacent to the first fabric ply.
 19. The method according to claim17, wherein a fabric ply of the wedge structure nearest the tank isoriented forty-five degrees relative to an axial direction of the tank.20. The method according to claim 17, wherein laying-up the tank skirtaround the wedge structure and the tank further comprises tapering athickness of the tank skirt such that the thickness of the tank skirt isgreater at the y-joint than away from the y-joint.